The present invention relates to self-propelled power implements, and more particularly to a speed control mechanism for a friction drive system of a self-propelled power implement.
Self-propelled power implements are commonly devices such as lawn mowers, lawn tractors, trimmers, tillers, or snow throwers, and are used for general outdoor applications such as landscaping, gardening, lawn care, or snow removal. These implements usually include an engine, and a means of transferring power from the engine to the wheels to propel the implement. Various types of transmissions are used to perform this task of transferring the power, and a friction drive system is an example of a transmission used for this purpose. Friction drive systems have proven to be an inexpensive, yet effective method of transferring power from the engine to the wheels and driving self-propelled power implements.
Friction drive systems commonly include two contacting discs: an output disc interconnected to the engine, and a friction disc interconnected to the wheels. These discs are often aligned transversely, and the rotation of the drive disc will cause the friction disc to rotate when the discs are engaged at a contact point. The output disc generally rotates at a relatively constant speed, and the friction disc rotates at a speed corresponding to the distance between the contact point and the center of the output disc.
Prior art friction drive systems have used a rigid structure to move the friction disc relative to the output disc, thereby moving the contact point and varying the speed of the friction disc and the wheels. These rigid structures frequently include a series of levers, bars, pivot joints, and sliding joints. A problem associated with the rigid structures is that the parts may become lodged or stuck, and may not pivot or slide smoothly. Further, the levers, bars, and joints must be properly aligned to function, and damage to even one of the parts can misalign and jam the shifting mechanism and render it inoperable. Adding to the problem is the fact that self-propelled power implements are often used for outdoor applications under harsh conditions.
The present invention provides a self-propelled power implement having a cable shifter system to adjust a friction drive system. The cable shifter system preferable requires relatively few moving parts and may be configured to smoothly move the friction drive system through an infinite number of settings.
The self-propelled power implement includes a frame, a pair of wheels coupled to the frame, an engine, an output disc, a friction disc, a flexible member, and a controller. The output disc is interconnected to the engine, and rotates in response to rotation of the engine""s output shaft. The friction disc contacts the output disc, and rotates in response to rotation of the output disc. The friction disc is coupled to the wheels and transmits the rotation of the output disc to rotation of the wheels. The rotation axis of the output disc is preferably transverse to the rotation axis of the friction disc.
The flexible member is interconnected between the controller and the friction disc. Movement of the controller is transmitted through the flexible member to actuate the friction disc. The friction disc moves radially with respect to the output disc, and this movement varies the speed of rotation of the wheels. In the preferred embodiment, the flexible member includes first and second cables that actuate the friction disc in first and second opposite directions, respectively, with respect to the output disc. Alternatively, the flexible member may include a single push-pull cable capable of actuating the friction disc in both the first and second directions.
The controller preferably includes a control bracket, a cable guide, and a shifter plate. The cable guide has a cam surface and is mounted for rotation with respect to the control bracket. Preferably, the flexible member at least partially winds around a portion of the cam surface. The shifter plate is mounted to the cable guide such that the cable guide is between the shifter plate and control bracket, and rotates with the cable guide with respect to the control bracket. The shifter plate has a peripheral portion that extends slightly beyond the cable guide and defines a channel between the shifter plate and control bracket that facilitates winding the flexible member onto the cam surface. A shifter is preferably interconnected to the shifter plate, and movement of the shifter causes rotation of the shifter plate and cable guide. Preferably, moving the shifter in a first direction will apply tension in the first cable, and moving the shifter in a second direction will apply tension in the second cable.
In the preferred embodiment, a spring biases the shifter plate towards the control bracket, and applies a sandwiching pressure on the cable guide. The shifter plate may be rotated with respect to the control bracket under the influence of an external force applied to the shifter, but the frictional forces caused by the spring resist movement of the shifter plate in the absence of such an external force. This potentially allows the shifter plate to be smoothly adjusted to an infinite number of positions with respect to the control bracket.